444 PATHOGENIC BACTERIA. most beautifully by Gram's method, by which it can be best demonstrated in tissues. Upon gelatin plates small white colonies are produced in from twenty-four to forty-eight hours. Under the microscope they are found to be spherical or elongate (lemon-shaped), finely granular, and lobulated like a raspberry or a mulberry. When superficial they form white, elevated, rather thick masses 1-2 mm. in diameter (Fig. 124). ^ In gelatin punctures a large white surface-growth FIG. 124.—Micrococcus tetragenus: colony twenty-four hours old upon the sur- face of an agar-agar plate; x 100 (Heim). takes place, but very scant development occurs in the puncture, where the small spherical colonies generally remain isolated. Upon the surface of agar-agar spherical white colonies are produced. They may remain isolated or may become confluent. Upon potato a luxuriant thick, white growth occurs. The growth upon blood-serum is also abundant, espe- cially at the temperature of the incubator. It has no distinctive peculiarities. The introduction of tuberculous sputum or of a most minute quantity of a pure culture of this coccus into white mice generally causes a fatal septicemia.